1. Field of the Invention
The invention relates to a laser blood-flow meter and a system for monitoring bio-data.
2. Description of the Related Art
Japanese Patent Application Publication No. 2002-45342 has suggested a laser blood-flow meter which irradiates laser beams to biological structure to allow the laser beams to be scattered in the biological structure, and detect power spectrum of scattered laser beams to thereby measure blood flow in the biological structure.
The suggested laser blood-flow meter measures or calculates blood flow by virtue of a speckle interference process making use of diffraction of laser beams scattered in biological structure.
Herein, speckle interference indicates, with respect to measurement of blood flow, a spotted noise or interference pattern obtained when scattered beam resulted when laser beams irradiated to biological structure are scattered with erythrocytes in blood are observed at a facet. The noise or interference pattern varies in accordance with movement of erythrocytes.
A laser blood-flow meter operates in accordance with such a principle as mentioned above. A laser blood-flow meter detects an interference pattern by irradiating laser beams to biological structure such that the interference pattern appears on a detection screen of a detector such as a photodiode, and measures blood flow, based on correlation between variance in the interference pattern and movement of erythrocytes.
Measurement of blood flow in a laser blood-flow meter is made with a sensor of the laser blood-flow meter being attached to a person to be monitored. Accordingly, when blood flow is measured continuously for a long time, a laser blood-flow meter would receive artifact noises caused by the person's slight movement and/or measurement environment.
The artifact noises often become extremely high in proportion with power spectrum of scattered beams, in which case, it is not possible to properly measure blood flow.
Thus, it was difficult or almost impossible to properly measure blood flow by applying a laser blood-flow meter to a monitor system which was necessary to receive for a long time blood flow data and biological data having correlation with the blood flow.
It is empirically known that blood flow in a head is different from blood flow in quarters. Hence, it has been said that blood flow in a head and quarters were necessary to be measured independently of each other, but it was not possible to do so because of the above-mentioned artifact noises.
Japanese Patent Application Publication No. 2001-120509 has suggested an apparatus for detecting power spectrum as a blood-flow signal, including a laser-beam source emitting laser beams in a longitudinal single mode, first means for stabilizing a wavelength of the laser beams, and second means for converting laser beams reflected from an object, into electric signals.
Japanese Patent Application Publication No. 1-256924 has suggested a method of diagnosing eyes including the step of irradiating laser beams to eyes wherein laser beams are received by a beam receiver through an optical fiber, a lens being disposed between the beam receiver and the optical fiber.
Japanese Utility Model Publication No. 37-31395 has suggested a lumen mirror including a beam irradiator, a beam collector and a detector.
Japanese Patent Application Publication No. 2-203838 has disclosed a probe for measuring blood flow, as prior art, including a prism for turning laser beams by 90 degrees.
Japanese Utility Model Publication No. 57-134658 has suggested a device for detecting whether a droplet exists on an object, including a beam block which prevents a beam irradiated from a beam emitter, from being directly received at a beam receiver.
Japanese Utility Model Publication No. 58-185203 has suggested an optical fiber sensor used for forward-scattered beams.